A mobile in-core instrumentation equipment (referred to as “TIP (Traversing Incore Probe) system,” hereinafter), which is one portion of an in-reactor nuclear instrumentation system in a boiling water reactor (BWR) nuclear power plant, is designed to measure a neutron flux level by moving a detector in an axial direction in a nuclear reactor when the nuclear power plant is in operation; obtain a reactor power distribution at each level of height in a direction of a core axis; and provide data that are used as a basis for calculating a reactor power distribution.
FIG. 13 is a block diagram showing an overall configuration of a conventional TIP system, as well as a nuclear reactor.
The TIP system transfers a TIP detector 540 into a plurality of TIP guide tubes 53, which are disposed in a reactor core 520 of a nuclear reactor 510. When the TIP detector 540 is pulled out from the top to the bottom of the reactor core 520, the TIP system generates a TIP position signal corresponding to a travel distance. In synchronization with the TIP position signal, the TIP system reads a TIP level signal, an LPRM level signal from a local power range monitor (referred to as “LPRM (Local Power Range Monitor)”, hereinafter), and an APRM level signal from an average power range monitor (referred to as “APRM (Average Power Range Monitor)”, hereinafter) to measure a neutron flux distribution of an in-core axial direction.
A process computer 590 and a TIP control panel 580 work together with each other and output a driving signal (insertion/pull-out signal for the detector) to a TIP driving equipment 570. Thereby, the TIP detector 540 is transferred.
In the TIP detector 540, the sensitivity thereof becomes attenuated by neutron radiation. Therefore, the TIP detector 540 is inserted into the nuclear reactor only when measurement takes place. When no measurement takes place, the TIP detector 540 is stored in a shielding container 560 outside of the nuclear reactor, thereby minimizing neutron radiation and preventing the attenuation of the detector's sensitivity.
FIG. 14 is a block diagram showing the configuration of a conventional TIP system, as well as signal processing.
Measuring a neutron flux level by the TIP system is performed in the following manner.
In a process computer 590, a display unit 600 and an operation input unit 611 are placed. An operator uses the above units to specify a TIP scanning signal (TIP scanning start/interrupt signal) and a TIP guide tube 530 (LPRM string) for which a neutron flux level is measured.
A signal input by the operator is processed by a TIP scanning unit 612 of the process computer 590, and then transferred to a TIP driving control unit 613 of a TIP control panel 580.
Moreover, on the TIP control panel 580, a TIP control panel operation section 581 is mounted. The operator is able to carry out an operation of making a driving request and a request of pull-out/insertion of the detector through a switch on the TIP control panel operation section 581. A TIP scanning signal from the process computer 590 is input into the TIP driving control unit 613, which outputs a driving signal (insertion/pull-out signal for the detector) to the TIP driving equipment 570.
Then, the TIP driving equipment 570 drives the TIP detector 540 in a direction corresponding to the driving signal.
Meanwhile, the neutron flux level measured by the TIP detector 540 is input, as a TIP level signal, into a TIP level reading unit 616 of the process computer 590 via a TIP level processing unit 614 of the TIP control panel 580.
Moreover, the height from the core top to core bottom of the TIP detector 540 is input, as a TIP position signal that is generated while the TIP detector 540 moves from the core top to the core bottom, into the TIP level reading unit 616 of the process computer 590 via a TIP position processing unit 615 of the TIP control panel 580.
The TIP level reading unit 616 of the process computer 590 reads a TIP level signal at a timing when the TIP position signal is turned ON (at a distance interval of an inch). Moreover, the TIP level reading unit 616 reads an LPRM level signal at timings of the core top and the core bottom, and an APRM level signal at timings of the core top, the core center and the core bottom; the signals are then stored in a TIP level data storage unit 617 of the process computer 590.
Then, the TIP data stored in the TIP level data storage unit 617 of the process computer 590 are displayed on the display unit 600 by the TIP scanning unit 612, and a log thereof is printed on a print unit 618. Moreover, the TIP data are transferred to a core performance calculation unit 619, where the TIP data are used as a basis for calculating a reactor power distribution.
FIG. 15 is a conceptual diagram of an axial-direction position of an assembly (referred to as “LPRM string”, hereinafter) of local power range monitors (referred to as “LPRM”, hereinafter).
LPRM strings are provided in the reactor core. Each of the LPRM strings contains one TIP guide tube 530 therein. Along an axial direction thereof, for each of the LPRM strings, four LPRM detectors “A”, “B”, “C” and “D” 661a, 661b, 661c and 661d, respectively are positioned and fixed.
FIG. 16 is a conceptual diagram of the arrangement of LPRM strings in the reactor core.
In the reactor core, a large number of LPRM strings are disposed. In the example of FIG. 16, the LPRM strings 660 are divided into five groups.
As for the TIP detectors 540, all the LPRM strings 600 are not covered by one TIP detector 540. In response to the above, five TIP detectors 540, “A”, “B”, “C”, “D” and “E”, are provided. Each of the TIP detectors 540 sequentially runs in about 10 LPRM strings.
An LPRM string 660 into which a TIP detector 540 is inserted is selected by rotating a rotating cylinder of a selection mechanism 550 shown in FIG. 13. At this time, selection is not made in such a way that a plurality of TIP detectors 540 are inserted into the same LPRM string 660.
Examples of related prior art documents are as follows: Jpn. Pat. Apple. Publication No. H05-11278, Jpn. Pat. Appln. Laid-Open Publication No. 2000-28782, Jpn. Pat. Appln. Laid-Open Publication No. 2006-145417, and Jpn. Pat. Appln. Laid-Open Publication No. H05-312991.
According to the conventional TIP system, the TIP control panel is an analog circuit. Therefore, data cannot be accumulated, and a TIP level signal and a TIP position signal are output from the TIP control panel to the process computer without being processed or stored.
Then, in the process computer, what is performed is a process of reading a TIP level signal (analog signal), which appears at a time when a TIP position signal (pulse signal) is turned ON, synchronously as a TIP level at a height thereof. However, because of hardware constraints of the process computer, the ON time of the pulse signal requires about 100 milliseconds.
Therefore, the driving speed of the TIP detector cannot be increased over 3 inches per second, which is why a reduction in plant start-up time cannot be achieved in completing the measurement of the TIP levels of the entire reactor core. Thus, the measurement is completed for about 15 to 30 minutes.
Another problem is that, due to the transfer lag of a signal or the delay of a timing at which the process computer detects that the pulse signal is ON, the accuracy of reading the TIP level data is not sufficient.
Furthermore, as for the data that serve as a basis for calculating the reactor power distribution, in synchronization with a TIP position signal, an LPRM level signal and an APRM level signal need to be input. However, the TIP control panel exists independently of an LPRM panel and an APRM panel. Therefore, the problem is that it is not possible to input an LPRM level signal and an APRM level signal in synchronization with a TIP position signal on the TIP control panel.
The TIP level data that are read into the process computer are used as basic data, which are used to improve the accuracy of power-distribution calculation in a process of calculating the reactor core's performance. However, in a conventional TIP system, it takes about one to two hours to measure the TIP levels of all the LPRM strings in the reactor core. Accordingly, during a process of measuring the TIP levels, there are changes in the states of the plant, which, for example, include a reactor thermal power, a core flow rate, a control-rod position, and the like. Thus, it is not possible to input TIP level data that accurately reflect the current power distribution. The problem is that the accuracy of calculating the reactor power distribution can deteriorate.
In the conventional TIP system, on the TIP control panel, a TIP level at a common guide tube (common string) is plotted by a mechanical pen recorder. From a chart of the pen recorder, the TIP level is read visually; the values of calibration current of the TIP detectors are adjusted (Gain adjustment) so as to have the same TIP level between each TIP detector at the common string. However, the accuracy of reading the TIP levels visually from the chart of the mechanical pen recorder is not sufficient. Another problem is that it takes a lot of time and effort for an operator to manually adjust the values of calibration current.
Moreover, in the conventional TIP system, the value of calibration current on the TIP control panel is confirmed before the deterioration of a TIP detector is assessed. Therefore, the problem is that it is difficult to determine the long-term trend of TIP deterioration, and to plan a replacement time of the TIP detector accurately.
Furthermore, in the conventional TIP system, between the TIP control panel and the process computer, as for each TIP, I/O cables are required for a TIP level signal, a TIP position signal, and the information about a selected LPRM string, i.e. a channel number, a contact signal associated with whether or not a TIP detector exists at a specific position such as the core bottom or top, or any other signal. A total of, for example, 135 cables are required for five TIP detectors. If the distance between the TIP control panel and the process computer is 100 m, the total length of the cables amounts to about 13 km. In this manner, large amount of cables are required.